Pesticide exposure in farmworkers from agricultural communities is linked to changes in the oral microbiome, according to a new study from the University of Washington School of Public Health.

In the study, published Nov. 11 in Applied and Environmental Microbiology, researchers sampled oral swabs from 65 farmworkers and 52 non-farmworker adults from the Yakima Valley in Washington state. Researchers took samples during the spring and summer, when farmworkers can undergo high pesticide exposures while working in recently sprayed orchards, and during the winter, when exposures tend to be quite low. Concurrently, they measured the participants’ blood levels of organophosphate pesticides.

Among farmworkers for whom the organophosphate pesticide azinphos-methyl was detected, researchers found "significantly reduced abundances of seven common taxa of oral bacteria, including Streptococcus, one of the most common normal microbiota in the mouth," said lead author, Ian Stanaway, a PhD candidate in the School’s Department of Environmental and Occupational Health Sciences. Changes in populations, species and strains of Streptococcus, as well as from the genus Halomonas, remained particularly low during the following winter.

Researchers also observed a pesticide-associated reduction in bacterial diversity in study participants during the spring and summer, which persisted into the winter. This suggests that "long-lasting effects on the commensal microbiota have occurred," according to the report.

Predictably, farmworkers had greater blood concentrations of pesticide, and greater changes in their oral microbiome than local, non-farmworking adults.

"The challenge becomes, what does this mean;" said principal investigator Elaine Faustman, also a professor in the School’s Department of Environmental and Occupational Health Sciences. "We don't know," she said, adding that "we depend on the microbiome for many metabolic processes."

Nonetheless, "in other studies, changes in species and strains of Streptococcus have been associated with changes in oral health," noted Stanaway.

The study subjects' enthusiasm for the research has been important to its success, said coauthor Beti Thompson, a professor in the School’s Department of Health Services and member of the Public Health Sciences Division of the Fred Hutchinson Cancer Research Center. The researchers followed the study participants for more than 10 years, she said. "They are very interested in all the effects of pesticides. They have contributed thousands of urine samples, tens of cheek cell samples, blood samples, saliva samples, and house and vehicle dust."